From 85a77eea8d7114675602a33d2e067fd7c4ad0624 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>
Date: Sun, 12 Jan 2014 11:38:56 -0500
Subject: [PATCH] core: do not segfault if swap activity happens when
 /proc/swaps is not open

In https://bugzilla.redhat.com/show_bug.cgi?id=969795 systemd crashes
in swap_dispatch_reload called from manager_loop becuase m->proc_swaps
is NULL. It can legitimately be NULL if something went wrong when
initially enumerating swap devices when starting the manager. This
is probably a sign of significant trouble, but let's do our best
to recover.
---
 src/core/swap.c | 45 +++++++++++++++++++++++++++++----------------
 1 file changed, 29 insertions(+), 16 deletions(-)

diff --git a/src/core/swap.c b/src/core/swap.c
index 147f710..f295b65 100644
--- a/src/core/swap.c
+++ b/src/core/swap.c
@@ -1068,14 +1068,40 @@ static int swap_load_proc_swaps(Manager *m, bool set_flags) {
         return r;
 }
 
+static int open_proc_swaps(Manager *m) {
+        if (!m->proc_swaps) {
+                struct epoll_event ev = {
+                        .events = EPOLLPRI,
+                        .data.ptr = &m->swap_watch,
+                };
+
+                m->proc_swaps = fopen("/proc/swaps", "re");
+                if (!m->proc_swaps)
+                        return (errno == ENOENT) ? 0 : -errno;
+
+                m->swap_watch.type = WATCH_SWAP;
+                m->swap_watch.fd = fileno(m->proc_swaps);
+
+                if (epoll_ctl(m->epoll_fd, EPOLL_CTL_ADD, m->swap_watch.fd, &ev) < 0)
+                        return -errno;
+        }
+
+        return 0;
+}
+
 int swap_dispatch_reload(Manager *m) {
         /* This function should go as soon as the kernel properly notifies us */
+        int r;
 
         if (_likely_(!m->request_reload))
                 return 0;
 
         m->request_reload = false;
 
+        r = open_proc_swaps(m);
+        if (r < 0)
+                return r;
+
         return swap_fd_event(m, EPOLLPRI);
 }
 
@@ -1225,22 +1251,9 @@ static int swap_enumerate(Manager *m) {
         int r;
         assert(m);
 
-        if (!m->proc_swaps) {
-                struct epoll_event ev = {
-                        .events = EPOLLPRI,
-                        .data.ptr = &m->swap_watch,
-                };
-
-                m->proc_swaps = fopen("/proc/swaps", "re");
-                if (!m->proc_swaps)
-                        return (errno == ENOENT) ? 0 : -errno;
-
-                m->swap_watch.type = WATCH_SWAP;
-                m->swap_watch.fd = fileno(m->proc_swaps);
-
-                if (epoll_ctl(m->epoll_fd, EPOLL_CTL_ADD, m->swap_watch.fd, &ev) < 0)
-                        return -errno;
-        }
+        r = open_proc_swaps(m);
+        if (r < 0)
+                return r;
 
         r = swap_load_proc_swaps(m, false);
         if (r < 0)